Transformer Coils Research Articles

Strength prediction of adhesively bonded ferrite pillar–tin bronze plate under axial shear loading

With the fast development of electronic, automotive and aerospace engineering in recent years, ferrite material has been widely used in devices including inductor, voltage transformer, filter and choke coil, etc. The proper characterisation on the mechanical capacity of the connection between ferrite and traditional metals has become a key issue for both industrial and academic fields. This work focused on the mechanical performance as well as fracture behaviour of adhesively bonded ferrite–tin bronze plate (FTBP), subjected to axial shear loading through experimental and numerical approaches. In the process, a new set of Arcan testing methods was developed for mechanical parameter determination of high flow epoxy adhesives. The material parameters of the epoxy adhesive connecting the ferrite pillar and bronze were experimentally determined. Curing mould was designed for the manufacture of the selected adhesive with high flowability in dumbbell tensile testing and Arcan testing under 0° and 90° loading directions. Quasi-static shear loading test was then conducted on bonded FTBP with a specially designed jig, and the failure surface was studied through optical microscopy and scanning electron microscopy (SEM) observations. Finite element (FE) modelling was carried out to simulate the loading process up to failure, where the crack propagation in the adhesive layer was modelled using cohesive zone model (CZM) with a bilinear traction-separation response. The experimentally measured and numerically simulated results of the adhesively bonded FTBP were compared with each other, proving the validity of the strength prediction approach developed in this work.Abbreviation: FTBP: Ferrite - Tin Bronze Plate; SEM: Scanning Electron Microscope; FE: Finite Element; CZM: Cohesive Zone Model; CIR: Cold In-place Recycling; DIC: Digital Image Correlation; DCB: Double Cantilever Beam; ENF: End-notched Flexure; PTFE: Polytetrafluoroethylene; CTOD: Crack Tip Opening Displacement; SDEG: Scalar Stiffness Degradation Variable; DOF: Degree of Freedom.

Thermal performance of heat sinks with variable and constant heights: An extended study

Heat sinks/fins are widely used in rapid heat removal processes like cooling of electronic devices, car radiators, transformer coils, nuclear reactors, etc. The thermal efficiency of the heat sinks mainly depends on the conductivity of the material used. In the present work, a comparative study is made on the thermal performance of heat sinks having variable and constant heights with respect to the bulk temperature, induced velocity, fin height/spacing/clearance, fin thermal conductivity and efficiency. A computational code based on SIMPLER algorithm is developed to solve the present problem. Results indicate that the variation of local Nusselt number against the flow direction shows higher values for the non-dimensional variable height heat sinks of 0.25 involving narrower fin spacing. It is also noted that consideration of finite conductivity of fin of 200 W/m-K and 75 W/m-K reduce the overall Nusselt number by 5.7% and 9.5% respectively while compared to an isothermal fin. Further, the use of variable height heat sinks coupled with a shorter fin height of 0.03 m indicates an improvement of thermal performance by around 225%.

A Low-Loss and High-Isolation Transformer-Based mm-Wave SPDT with Integrated Fan-out Wafer Level Packaging

This paper proposes a low-loss and high-isolation transformer (TF)-based mm-wave single-pole double-throw (SPDT) switch. The center-tapped technique is employed at the secondary coil of TF to improve isolation performance. The TF is implemented with the metals in redistribution layers (RDLs) in integrated fan-out (InFO) wafer level packaging technology to obtain low insertion loss (IL) and small chip size as the TF usually dominates the area of SPDT. The control device of the SPDT is realized in 40[Formula: see text]nm bulk CMOS process. The simulated result shows the proposed SPDT achieves a minimum IL of 1.34[Formula: see text]dB and the IL is less than 2.2[Formula: see text]dB at 24–31[Formula: see text]GHz. The isolations are better than 27[Formula: see text]dB between two double-throw ports and better than 20[Formula: see text]dB between single-pole and double-throw ports, respectively. The proposed SPDT has a compact silicon size of 220[Formula: see text][Formula: see text] (with PADs) and its return losses are better than [Formula: see text]9[Formula: see text]dB at 24–31[Formula: see text]GHz and. This work explores a new chip-package co-design method for the SPDT and may have some guidance for the co-design of SPDT and antenna in package (AiP).

Highly Flexible High-Efficiency Multiple-Resonant Wireless Power Transfer System Using a Controllable Inductor

Low- $Q$ resonant converter, such as series–series resonant converter, series resonant converter, and parallel resonant converter (PRC), are highly flexible and highly tolerant to coil misalignments. However, these kinds of topologies cannot be employed to the wide air-gap, low-coupling transformers because of their inadequate magnetizing inductance. On the other hand, high- $Q$ multiple-resonant converters such as series-PRC) and series-SPRC are very suitable for low-coupling compact wireless transformer applications. However, because these multiresonant topologies have several resonant pairs resonating at a single frequency, these parameter values ought to be consistent throughout the operating conditions to resonate at the same frequency. However, since the wireless power transfer (WPT) applications are required to be flexible and convenient to the customers, the wireless transformers are not supposed to be rigid and stationary. To solve the problem, a controllable inductor for a high- $Q$ multiresonant WPT system is proposed to extend the soft switching region and to keep the resonant circulating energy minimum even at resonant mismatch conditions caused by the misalignments or temperature variations of the wireless transformer coils. The performance enhancement of the multiple-resonant wireless converter is validated using the proposed controllable inductor technique, and also the feasibility of the proposed technique is proven under different mismatch conditions through 200-W hardware experimental results.

Heat-resistant insulation film containing clay and wood components

In this paper, we prepared a novel organic–inorganic nanocomposite film with excellent insulation properties relative to the polyimide film in mild-processing conditions. The main component of the film is clay mineral and wood component, i.e., the layered silicate and poly(ethylene glycol)-modified lignin derivatives. In the nanocomposite film, an interlayer of silicate was bound by triethanolamine. Furthermore, the lignin derivatives filled the voids of the layered silicate, producing a defect-free densely packed nanocomposite film. This unique structure of the nanocomposite film provides high-thermal stability, a low thermal expansion coefficient of film consisting of clay and lignin derivatives, low gas transmittance rate, low volume/surface resistivity, and high dielectric breakdown voltage. The obtained nanocomposite film was installed in a planar-type transformer where it acted as an insulation film in the transformer coil with high dielectric breakdown voltage.

Theoretical and Simulation Study on On-line Monitoring Technology of Transformer Short-Circuit Impedance

Based on the equivalent circuit of transformer, this paper deduces the calculation method of short-circuit impedance of three-phase transformer based on multiple measurement data. Taking a single-phase transformer as the research object, the ‘magnetic field-circuit’ simulation model is established. The normal operation and winding deformation caused by different axial displacements are simulated and analyzed. The results show that short-circuit impedance changes when transformer winding is axially deformed, and the degree of change is related to the degree of deformation. Compared with the normal situation, the short-circuit impedance increases by 52.1% when the four transformer coils are moved 15 mm each. Therefore, on-line monitoring of the transformer short-circuit impedance can reflect the abnormal deformation of the transformer winding to a certain extent.

Transforming characteristics of the Rogowski coil current transformer with a digital integrator for high‐frequency signals

The Rogowski coil current transformer is widely used in intelligent substations for its rapid response, wide bandwidth measurement, and non-magnetic saturation. In most cases, it works with a digital integrator to restore the differential signal output by the coil. However, its output waveform can be deformed when transforming high-frequency signals generated in the transient process of the power system. The working process of the Rogowski coil current transformer is presented, including Rogowski coil head transferring, analogue filter filtering, analogue-to-digital converter sampling, and digital integrator restoring. The reason for the waveform deformation when transforming high-frequency signals is investigated by theoretical derivation. In order to show the waveform deformation phenomenon, an experiment is devised and the results output by the Rogowski coil transformer and low power current transformer are compared and analysed. Several measures to improve the output waveform deformation are proposed, such as increasing the sampling rate of the converter, decreasing the cut-off frequency of the filter, or replacing the digital integrator with the analogue integrator. The researches provide important guidelines for the application of the Rogowski coil current transformer with the digital integrator in the case of frequency aliasing.

Heat transfer enhancement from power transformer immersed in oil by earth air heat exchanger

In this study, the modelling of power transformer with (250 kVA) by using (ANSYS17.1/FLUENT) code program was done. The power transformer was connected with earth air heat exchanger to decrease the temperature of (oil, core, and coils) of transformer which will increase its efficiency for preventing the damage and/or failure. The case study used the weather conditions of Nasiriya city, Iraq, at July 1st with 50?C as maximum ambient temperature and full electrical load of the power transformer. In addition to different pipe diameter, length of earth air heat exchanger and different air velocity entering to pipe. The results showed the temperature of (oil, core, and coils) for power transformer decreased with increase the pipe length and earth air heat exchanger depth underground. The air velocities inlet to earth air heat exchanger that used in the study were (2, 4 , and 6 m/s, respectively) and the results showed the increasing of air velocity inlet to earth air heat exchanger should decrease the temperature of (oil, core, and coils) for power transformer and increase the thermal conductivity of oil. The study concluded when using earth air heat exchanger in the power transformer and performance of power transformer will be increasing and led to decrease the temperature of oil about (18.5?C).The results showed a significant convergence with previous researches.

Creating 3D printed magnetic devices with ferrofluids and liquid metals

Combining electrical and magnetic materials in the same part has been a challenge in 3D printing due to difficulties co-printing complex materials in many additive manufacturing processes. Past 3D printed inductors and other similar magnetic devices have therefore either lacked the magnetic materials necessary for improved performance, or required sintering at high temperatures for extended periods, beyond the capability of most 3D printable polymers. In this work, we demonstrate a room temperature process for incorporating conductive and magnetic materials into the same 3D printed device. A multi-stage fabrication process based on 3D printing followed by fill with magnetic and conductive fluids is proposed. Multi-layer microfluidic channels for magnetic passives are first printed in a stereolithography process. The microfluidic systems are then filled with room temperature liquid metal, a gallium alloy liquid at room temperature, and ferrofluid to create inductors, transformers and wireless power coils. Through the addition of ferrofluid as a magnetic material, increases in inductance density by nearly a factor of three were demonstrated, in addition to coupling improvements for transformer and wireless power coils compared to the devices before magnetic fill.

A Study of Electrical Aging of the Turn-to-Turn Oil-Paper Insulation in Transformers with a Step-Stress Method

This study investigates the electrical aging characteristics of oil-paper composite insulation. In this paper, a coils model and test system for oil-paper transformer insulation are designed. The electrical aging tests of the model coils at room temperature and operating temperature are performed using the step-stress method. A new method for estimating the unknown parameters in the inverse power exponent model is proposed, and the inverse power model life formula expressed by voltage and electric field strength is obtained. Considering the electrical aging process at the operating temperature, the allowable field strength of the inter-turn insulation of oil-immersed transformers can be improved. The new parameter estimation method proposed in this paper can be used to calculate the unknown parameters of the step-stress solid insulation aging model. This method has a clear physical meaning and can be solved easily. When the stressed voltage is below a certain threshold value, the life of the transformer coil turn-to-turn insulation grease oiled paper model is longer at operating temperatures compared with that at room temperature; when the voltage is higher than the threshold, it presents the opposite tendency.

U‐shaped stacked structure monolithic transformer for efficiency improvement

AbstractThis article presents a novel monolithic transformer (TF) structure, which is designed to improve TF efficiency by enhancing the quality factor of the metal trace. When the number of thick metal layers is limited in semiconductor technology, it is necessary to use thin metals that have lower quality factors to form the TF coil, which degrades TF efficiency. To overcome this limitation, supplementary walls of metal and a via are connected along both sides of the thin metal to form a U‐shaped metal trace, which in turn improves the quality factor and TF efficiency. The proposed structure does not require additional metal layers, other than the metal layers used in the TF configuration. Thus, the proposed structure is widely applicable to all semiconductor technologies, including those that provide only a small number of metal layers. To assess and validate this proposed structure, we fabricated a set of TFs including conventional structures using gallium arsenide (GaAs) technology, which is the most widely used technology in mobile power amplifier (PA) fabrication. The proposed structure was successfully demonstrated to effectively improve the TF efficiency by as much as 8.6% and 6.5% in comparison to a conventional planar structure and a stacked structure, respectively.

Increase in Robustness against Effects of Coil Misalignment on Electrical Parameters Using Magnetic Material Layer in Planar Coils of Wireless Power Transfer Transformer

Utilization of wireless power transfer in light rail transits is seen as one solution for electrification of lines. The main advantage of this supply system is the reduction of installation; moreover, the alignment between the transmitter coil in the track and the receiver coil in the train should be perfect in order not to affect the power transfer. To reduce the effects of misalignment on the input and output electric parameters of the system, a new planar core and coil design, called hybrid intercore coil, is proposed. The proposed design uses a magnetic material layer between the windings in the inner half of the coil to create a non-uniform magnetic field distribution, which makes the system more robust against the effects of coil misalignment on the system current and voltage. Simulations with finite element method software were conducted to compare designs. The results show that the proposed design is less susceptible to the effects of misalignment and is more efficient. Prototype cores were constructed to verify the simulation results. Measurements show a smaller input overcurrent and output overvoltage when operating in resonance mode. The proposed design reduced the effects of coil misalignment on electrical parameters.

Alternative approaches and dynamic analysis considerations for detecting open phase conductors in three phase power systems

Open phase conductors in three-phase power systems can be difficult to detect with conventional protection relay schemes. Such events can have adverse consequences to power system equipment reliability and performance. The resultant voltage unbalance associated with open phase events can cause excessive heating in transformer core and coil assemblies and tanks, reduce the available starting and running torque of motors, increase motor acceleration time, cause inadvertent tripping of critical loads, and thermally damage plant equipment.Power system response to an open phase condition is highly dependent on a number of factors, including the type of open phase condition (events involving one or two phase conductors, coupled with or without a ground), the location of the open phase, the topology of the power system, transformer core design and winding connections, and type and magnitude of system loading.This paper briefly describes industry operating experience with open phase events. It summarizes the various alternative approaches for detecting open phase conductors on large station service transformers. Dynamic modeling considerations and techniques are described and a summary of analytical results which convey the challenges, advantages, and disadvantages associated with different detection strategies are presented. The role symmetrical components and sequence components can play in understanding the impact of open phase conditions on power system equipment also is discussed.

Theoretical and Experimental Study on Mechanical Force of Transformer Coil Short Circuit

As one of the most important components of transmission equipment in electric power field, power transformer bears the important task of energy conversion, power distribution and energy transfer. Because generated a huge force in transformer winding by its interior circuit excitation, it would be taken place easily to distortion, collapse and other damage of its structure, which brings a large safe and reliable problem. The lack of mechanical strength of the coil, which cannot withstand the sudden short-circuit current impact, led to the break of insulating layers, is one of the main causes in transformer failure. In this paper, it is discussed that theoretical and experimental study on mechanical force of transformer coil short circuit. According to the structural mechanics, the calculation of the contacted pressure between the coils is attained by building the contacted model. And the experimental system is been designed, which has a servo control system. Compared the theoretical and the Experimental data, the best accurate computed method for contacted pressure is obtained. It is helpful to improve the resistance ability for short circuit of transformer, and provide guarantee for the safe operation of the transformer.

A Witricity-Based High-Power Device for Wireless Charging of Electric Vehicles

In this paper, a Witricity-based high-power device is proposed for wireless charging of electric vehicles. According to the specific requirements of three-stage charging for electric vehicles, four compensation modes of the Witricity system are analyzed by the Loosely Coupled Theory among transformer coils and the Substitution Theorem in circuit theory. In addition, when combining voltage withstand levels, the current withstand capability, the switching frequency of electronic switching tubes, and the features of the resonant circuit, the series-parallel (SP) compensation mode is selected as the best compensation mode for matching the capacitor of the system. The performances of coils with different ferrite core arrangements are compared by simulations and models. The feasibility of the system is verified theoretically and the system functions are evaluated by the joint simulation of Simplorer and Maxwell. Finally, a Witricity-based high-power device is proposed as designed, and the correctness of theoretical analyses and simulation results are verified.

Optimization of contactless transformer coupling transmission system by Taguchi method

ABSTRACTA contactless transformer coupling (CTC) transmission system transmits electric energy via an alternating magnetic field through an air-gap. The transmitted power can be enhanced by the application of resonant effects. Transmitting and receiving coils are usually single layer solenoids with series capacitors, which, in combination, allow the receiving element to be tuned to the required transmitter frequency. An input DC source is used to obtain high-frequency AC signal through the standardized half-bridge DC/AC switching circuit. Further, the high-frequency signal passes through matching transformer and contactless coupling induction coil, which can be considered as an isolated input and output stage. Coupling must be tight to achieve high efficiency. This paper then applies the methods of Taguchi parameter design forthe contactless transformer coupling transmission system, which enhances the output voltage, loss factor, and output efficiency of the transmission system. The results of measurement verify the feasibility of this structure in the experiment.

구형파 변조된 경두개 자기자극을 이용한 쥐의 감각피질 자극실험

본 논문에서는 쥐 뇌의 감각 피질을 자극하기 위해 변조신호를 이용하여 경두개 자기자극(TMS) 동물실험을 수행하였다. 제안한 TMS 시스템은 인버터, 변압기, 커패시터, 가변 인덕터, 자극 코일로 구성되어 쥐 뇌의 감각피질에 약 1.5 mT의 자기장이 생기도록 시스템을 설계하였다. 자극 신호는 구형파 변조되었으며, 반송 주파수는 85~91 kHz의 범위로 변화시키며, 자극 효과를 관찰하였다. 자극 결과 반송 주파수가 89 kHz 미만일 때에는 자극의 효과를 볼 수 없었고, 반송 주파수가 89 kHz 이상일 때에는 압력 자극에 반응하는 역치 값이 낮아지는 효과를 볼 수 있었다. In this work, a transcranial magnetic stimulation(TMS) experiment on animals is performed to stimulate the brain cortex of the mouse using modulated signals. The proposed TMS system is composed of the inverter, transformer, capacitor, variable inductor, and stimulation coil to generate 1.5 mT magnetic field in the brain cortex of the mouse. The stimulation signal is modulated to square wave where the carrier frequency is swept from 85 to 91 kHz to investigate the stimulation effect. The experimental result shows that when the carrier frequency of the stimulation signal is lower than 89 kHz, the reaction of the mouse does not change while the stimulation signal which has the carrier frequency higher than 89 kHz results in decreasing the threshold of the stimulus for the pressure.

Loosely Coupled Transformer Coil Design to Minimize EMF Radiation in Concerned Areas

Wireless power transfer (WPT) technology as a convenient and reliable charging method, its electromagnetic field (EMF) radiation, and its compliance with human electromagnetic exposure limits have recently been studied. Different from the current research, which validates the EMF radiation level of a predesigned WPT system, this paper presents the loosely coupled transformer design method to minimize the EMF in the concerned area. The energy storage in the primary and secondary coils is studied for all popular compensation topologies in recently reported research. The coil of the loosely coupled transformer is designed with the S-S compensation topology as an example. The EMF radiation level is optimized to below the International Commission on Non-Ionizing Radiation Protection guideline in the concerned area. A 3.3-kW WPT system for electric vehicle wireless charging with an LCC-LCC compensation topology is designed with detailed process and experiment results, verifying that the EMF radiation is controlled as designed. The numerical analysis of human exposure is performed with the finite-element method, and the results show compliance as expected.

Vector-Potential Transformer With a Superconducting Secondary Coil and Superconducting Magnetic Shield

We created a complex coiled coil (vector-potential coil) to generate a curl-free vector potential. The device comprises a long flexible solenoid wound around a hollow nonmagnetic nonconducting cylinder; the entire coil has a coiled-coil structure. A straight superconducting BiSrCaCuO (BSCCO) wire was placed in the hollow cylinder at 77 K to serve as a secondary coil of a vector-potential transformer. We detected a nonmagnetic voltage induced between the ends of the secondary coil. The open-circuit voltage that was detected was the same as that of a normal conductor, i.e., a copper wire, which was also used as the secondary coil. Moreover, we replaced the hollow cylinder with a hollow superconducting BiPbSrCaCuO cylinder, which provides an ideal magnetic shielding. Even with the secondary coil inside the hollow BiPbSrCaCuO magnetic shield, the voltage induced across both BSCCO and copper secondary coils was identical to that measured when using the hollow nonmagnetic nonconducting cylinder.

A Stagger-Tuned Transimpedance Amplifier

A new transimpedance amplifier (TIA) design procedure using stagger tuning with inverted transformer coils is described in this paper. A broadband TIA, realized using the proposed staggered design technique that enhances the transimpedance limit and the bandwidth while only adding small passband gain ripple, was implemented in a 0.13- ${\mu }\text {m}$ standard CMOS process. The TIA achieves a 3-dB bandwidth of 33 GHz with a 150 fF photodiode capacitance. The TIA transimpedance gain is $43.8~{\text {dB}}\Omega $ with ±8 ps group-delay variation over the entire bandwidth. The circuit occupies an active area of ${250~\mu }\text {m}\times 260~\mu \text {m}$ and consumes 9 mW from a 2 V supply. Despite operating with much larger photodiode capacitance, the TIA achieves the highest figure of merit, and occupies smaller area while consuming the least amount of power among previously published TIAs designed for the same data rate in similar technologies.